Conventionally, there are foaming alcoholic beverages such as beer and low-malt beer which use malt as a main material. The malt used as a main material significantly contributes to, for example, the flavor, the foam quality (foam stability, foam generating property), and the fermentability of beer and low-malt beer.
On the other hand, beer-flavored foaming alcoholic beverages without using barley, wheat and malt have been developed and are sold in the marketplace. Such beer-flavored foaming alcoholic beverages have a flavor, a foam stability and a foam generating property that are similar to those of beer or low-malt beer.
More specifically, they have a characteristic refreshing flavor which is obtained by producing a pre-fermentation liquid by using a syrup containing sources of carbon, sources of nitrogen such as an amino acid containing substance, water, and hops along with adding a raw material for improving foam quality or a flavoring agent if necessary, and performing alcohol fermentation on the pre-fermentation liquid by adding brewers' yeasts in a same manner performed in a typical process for producing beer.
These foaming alcoholic beverages commonly have characteristics such as foam quality (e.g., foam generating property, foam stability) and a unique flavor as represented by beer. One important factor related to the improvement of the unique flavor (resembling beer or low-malt beer while having a refreshing flavor) and the foam qualities is protein. In beer, for example, proteins included in malt and sub-materials are digested by enzymes which decompose the protein (e.g., protease) included in malt during a malting and mashing process, and become water-soluble protein and amino acids; they, basically, become sources of nitrogen for serving as nutrition sources of brewers' yeasts, and at the same time, contribute to improvement of foam quality and flavor quality. Also, sources of nitrogen are used as materials for use in the above beer-flavored foaming alcoholic beverages. The suitable sources of nitrogen are materials including amino acid. For example, after extracting a starch ingredient from corns, potatoes, peas, soy beans, rice and so on, then passing the starch ingredient through a decomposition process, a part of nitrogen ingredients is decomposed into amino acid.
Also, proteins which are extracted from peas and soy beans, soy bean saponin, a yucca saponin, a guillai saponin, a tea saponin, plant extraction saponin system materials such as Koma carrot saponins, egg white peptide, protein system materials such as cow serum albumin, xanthan gum, carrageenan, pectin, Arabia gum, agar, thickeners such as gellan gum and alginic acid ester are used, according to necessity, as a substance for improving foam quality.
However, the above sources of nitrogen can be used not only for beer-flavored foaming alcoholic beverages but also for low-malt beer. Thereby, they can contribute to improving flavor and foam quality.    Patent Document 1: Japanese Laid-Open Patent Application No. 2001-37462    Patent Document 2: Japanese Laid-Open Patent Application No. 2004-81171